This is a GREAT site!!!! i wish I found this sooner.

Well, I am about to start making my own MDF zoned vacuum table. I came up with one question though....

I understand on making the seperate zones which can close off by valves as needed, sealing the top and of the plenum, and sealing the sides of the spoilboard to avoid leaks and hold the vacuum. If I have a vacuum table of 4'x8' and the sheet that is being cut is 36"x50" would the rest of the vacuum table need to be covered with a non porous material to not let the air leak in through the spoilboard?

Since the spoilboard is porous wouldn't the air leak in through the surface and travel horizontally into the area that is being used even though the other zones are turned off and there would be a loss in vacuum? Or does the vacuum only travel vertically through the spoilboard?

I would think that the zones would only be seperated and pull a complete vacuum vertically to hold down the item if the spoilboard was cut into pieces the size of each zone and the sides sealed to prevent leaks from other zones. I've looked at many very detailed vacuum table layouts which helped with the construction of the table but all of them use a single sheet of LDF as a spoilboard.

Could someone please help me out with this question? Thanks.